Implantable medical devices such as pacemakers and ICDs are typically configured to sense electrical cardiac signals within a patient as intracardiac electrograms (IEGMs). An IEGM is representative of electrical signals emitted by active cardiac tissue as detected by electrodes placed in, on or near the heart. The IEGM is then used to control the operation of the device. For example, the IEGM may be examined to detect arrhythmias or other abnormal cardiac events such as premature atrial contractions (PACs) and premature ventricular contractions (PVCs) so that appropriate thereby can then be delivered to the patient by the device. The portions of the IEGM that correspond to abnormal cardiac events are preferably digitized and recorded within the implanted device, along with an indication of the date and time, for eventual transmission to an external programmer for display thereon, typically during follow-up sessions with a clinician. The clinician can then review the IEGMs recorded within the patient during the abnormal cardiac events to verify that the events were indeed abnormal and to confirm that appropriate therapy was delivered. The clinician can also reprogram the device, if warranted.
The implanted device is also equipped to detect various normal cardiac events within the IEGMs, such as atrial depolarization events (P-waves), ventricular depolarization events (R-waves or QRS-complexes), ventricular repolarization events (T-waves) and to generate event marker codes representative of these and other events for recording within device memory for eventual transmission to the external programmer. The external programmer then generates event marker icons based on the event code and displays the icons along with the IEGM signals. Exemplary event markers are: “P” for a sensed depolarization event in the atria; “R” for a sensed depolarization event in the ventricles; “A” for a paced depolarization event in the atria, and “V” for a paced depolarization event in the ventricles. Along with event markers, the programmer may also display numerical values indicative of heart rate or indicative of various measured intervals between atrial and ventricular events, based on still further IEGM information recorded and transmitted by the implantable device.
U.S. Pat. No. 5,431,691, to Snell et al., entitled “Method and System for Recording and Displaying a Sequential Series of Pacing Events” provides a description of the operation of an exemplary pacemaker and external programmer, including a detailed description of the generation, transmission and display of IEGM data and event markers. See, also, U.S. patent application Ser. No. 11/740,720, now U.S. Pat. No. 7,778,699, of Ferrise et al., entitled “System and Method for Trigger-Specific Recording of Cardiac Signals using an Implantable Medical Device.” See, also, U.S. Pat. No. 6,633,776 to Levine et al., entitled “Method and Apparatus for Generating and Displaying Location-Specific Diagnostic Information using an Implantable Cardiac Stimulation Device and an External Programmer.” Herein, IEGMs, corresponding event markers, and any other pertinent data stored therewith are collectively referred to as “IEGM data.”
Current state-of-the-art devices permit IEGMs to be sensed and recorded using several possible electrode configurations. For example, one IEGM might be derived from voltage signals sensed between the right ventricular (RV) tip electrode and the RV ring electrode; whereas another IEGM might be derived from voltage signals sensed between the right atrial (RA) tip electrode and the housing or “can” of the device itself. Each electrode combination thereby provides a different representation of the electrical conditions of the heart, which is particularly helpful to the clinician. In this regard, if the patient is subject to atrial arrhythmias, it may be advantageous to specifically examine atrial IEGM data, such as an AR TIP-can IEGM; whereas, if the patient is subject to ventricular arrhythmias, it may instead be advantageous to examine ventricular IEGM data, such as a VR TIP-VL TIP IEGM. Lead systems often include numerous electrodes, thereby providing a wide range of choices of electrode pairs for recording IEGMs. In addition to the aforementioned AR TIP, VR TIP, VL TIP and device housing electrodes, lead systems for use with state-of-the-art devices may include: a right atrial ring electrode (AR RING), a left ventricular tip electrode (VL TIP), a left atrial ring electrode (AL RING), a left atrial coil (AL COIL), a right ventricular coil (RV COIL), a left ventricular tip electrode (VL TIP), a left ventricular ring electrode (VL RING), left ventricular coil (VL COIL). Typically, IEGMs that are sensed between the device housing and one of the electrodes implanted on or within the heart, such as between the VR TIP and the device housing, are referred to as “unipolar” IEGMs. IEGMs sensed between a pair of the electrodes both implanted on or within the heart, such as between the VR TIP and the VR RING, are referred to as “bipolar” IEGMs.
As can be appreciated, given the memory and power limitations within an implantable device, it is not typically feasible to sense and record IEGM data from every possible pair of electrodes. Accordingly, clinicians are invited to select particular electrode configurations for recording IEGM data of particular interest. For example, the clinician might select two atrial channel IEGMs (i.e. IEGMs derived primarily from atrial electrodes) and two ventricular channel IEGMs (i.e. IEGMs derived primarily from ventricular electrodes) for recording. Moreover, it is not ordinarily feasible to record each of the selected IEGMs at all times. Rather it is typically feasible only to record IEGMs and corresponding event markers during periods of interest, such as during an arrhythmia or other abnormal cardiac event. Accordingly, state-of-the-art devices are configured to record the selected IEGM data only in response to the detection of arrhythmias or other anomalous events of interest (PACs, PVCs, etc.), or following an automatic mode switch (AMS) from one pacing mode to another. The events triggering the recording of IEGMs are referred to as “triggers.” In state-of-the-art devices, the clinician is invited to select the particular triggers to be used by the device in activating the recording of the IEGM data.
In many cases, it is also desirable to record IEGM data prior to the trigger, as well as just following the trigger, so that the clinician can review the conditions leading up to the trigger and the conditions following the trigger. This is particularly important insofar as arrhythmias are concerned as the clinician usually wants to be able to review IEGM data prior to the onset of the arrhythmia so as to more readily diagnosis the cause of the arrhythmia. Accordingly, many state-of-the-art devices are configured to allow so-called “pre-trigger IEGMs” to be saved along with IEGMs recorded during an arrhythmia. Briefly, the device continuously detects and records IEGMs in a memory buffer, such as a circular first-in/first-out queue. If an arrhythmia is detected, the IEGMs recorded just prior to the onset of the arrhythmia are transferred from the memory buffer to long-term memory, so that the pre-trigger IEGMs can be saved along with IEGMs recorded during the arrhythmia itself for subsequent review by the clinician. In this manner, IEGM data detected during the period of time leading to the onset of the arrhythmia is saved in long-term memory for subsequent review by the clinician, without requiring all IEGMs to be saved in long-term memory at all times. Pre-trigger IEGMs can also be transferred to long-term memory upon detection of other selected triggers, such as pacemaker-mediated tachycardias (PMTs), PVCs, AMS events, etc. A particularly effective technique for implementing pre-trigger memory is set forth in U.S. Pat. No. 7,421,292 to Kroll, entitled “System and Method for Controlling the Recording of Diagnostic Medical Data in an Implantable Medical Device.”
Thus, state-of-the-art implantable medical devices provide for the recording of pre-trigger and post-trigger IEGMs upon detection of particular diagnostic triggers chosen by the clinician or other clinician. Moreover, the clinician can also specify the particular electrode pairs for use in sensing the IEGMs to be recorded. This provides considerable flexibility to the clinician in obtaining IEGMs of interest while also reducing the amount of data the device itself needs to record. However, there is considerable room for further improvement.
It has been found that a large amount of stored IEGM data is falsely triggered, i.e., the “abnormal” events triggering the recording of IEGM data are often not actual abnormal events. For example, events initially deemed to be PACs or PVCs might instead have just been the result of far-field sensing of P-waves or R-waves (FFRWs) from other cardiac chambers. Since stored IEGMs typically require a significant amount of memory, such “false positives” can result in the use of substantial device memory to store unhelpful or useless information. Worse, in at least some cases, a false detection can result in the delivery of unneeded or inappropriate therapy.
In other cases, the implanted device might fail to detect abnormal cardiac events that actually occurred within the patient. Such “false-negatives” can result in a failure to deliver needed therapy. Moreover, because the recording of IEGM data is not triggered unless an abnormal event is detected, false-negatives prevent important IEGM data from being properly recorded and then sent to the external programmer for clinician review. As such, the clinician might be unaware of that certain abnormal events are occurring within the patient.
Accordingly, it is highly desirable to provide techniques for reducing or eliminating the false-positive detection of events of interest, particularly abnormal events, to prevent delivery of inappropriate therapy and to prevent recordation of unneeded IEGM data. It is also highly desirable to provide techniques for reducing or eliminating false-negatives to better ensure proper delivery of therapy and to ensure proper recordation of important IEGM data. It is to these ends that aspects of the invention are generally directed.